Zinc alloy electroplating baths and processes

ABSTRACT

The present invention relates to the electrodeposition of zinc nickel alloy on a variety of electrically conducting substrates in a medium which seeks to provide improved deposit distribution and operable current density range. This is achieved through a bath comprising zinc ions, nickel metal ions, and a suitable combination of one or more urea based polymers and non-polymeric complexing agents capable of holding nickel metal ions in alkaline solution and an electrolytic process whereby the bath is used to electrodeposit zinc nickel alloy on electrically conducting substrates.

FIELD OF THE INVENTION

The present invention relates generally to improvements in theelectrodeposition of zinc nickel alloys from aqueous alkaline platingbaths and to new additives for use in such electrodeposition processes.

BACKGROUND OF THE INVENTION

Electrodeposition of zinc and zinc alloys based on alkaline platingbaths has been known for many years. However, it is not possible toproduce a commercially acceptable deposit from a simple sodium zincateelectrolyte as the deposit is powdery and dendritic. For this reason,various additives have been proposed to provide improved deposition,such as cyanides (which have obvious environmental problems) andpolymers of amines and epichlorohydrin which act as grain refiningadditives. These polymers are limited to usage in baths havingrelatively low concentrations of zinc because it is not possible to Fprevent uncontrolled deposition of zinc at higher metal concentrations.Also, electroplating processes using these additives tend to have poorcathode efficiency, a narrow bright range, a narrow operating window,and tend to produce pitted and “burnt” deposits. Plating compositions ofthis type are described in U.S. Pat. No. 2,080,479 to Hoff and U.S. Pat.No. 4,861,442 to Nishihama and U.S. Pat. No. 4,983,263 to Yasuda et al,the content, each of which is herein incorporated by reference.

More recently, additives have been proposed which allow higher zincconcentrations to be used, which have significantly reduced burning andpitting and which allow a wider range of operating parameters. Further,the additives enable an excellent deposit distribution (that is,evenness of the deposit across the article being plated, irrespective ofits shape in particular areas). This maximizes the efficiency of zincusage. These additives are based generally on polyquaternary aminecompounds and are described in U.S. Pat. No. 5,435,898 and U.S. Pat. No.5,405,523, which also provide further discussion of the prior art andthe content each of which is herein incorporated by reference.

Plating compositions for depositing zinc nickel alloys from alkalineelectrolytes are well known and are described in US patents such as U.S.Pat. No. 6,468,411, U.S. Pat. No. 5,417,840, U.S. Pat. No. 4,861,442,and U.S. Pat. No. 4,889,602, which also provide further discussion ofthe prior art and the content each of which is herein incorporated byreference. Plating solutions that provide an alloy compositioncontaining from 12% to 15% nickel are most desirable giving optimalcorrosion performance. This alloy is currently utilized by manyautomotive manufacturers.

The zinc to nickel metal concentration ratio of alkaline zinc nickelplating baths of the prior art producing zinc nickel alloys of >12% Nicontaining oligomeric or polymeric amine species is of the order 7:1 to10:1. This is consistent with the ratio of nickel in the desired alloyof 12% to 15% and corresponds to more ‘normal deposition.’ Unexpectedlyit has been found that baths of the present invention producing zincnickel alloys of 12% to 15% Ni have a zinc to nickel metal concentrationratio of the order 1.5:1 to 2.5:1. Thus the zinc to nickel metalconcentration ratio is not consistent with the alloy deposited. Thistype of deposition is described as ‘anomalous deposition’ and isgenerally typical of the acid zinc nickel based electrolytes describedin US patents and applications such as U.S. Pat. No. 4,699,696 and US2003/0085130 A1.

Further it is known that in practice used baths of alkaline zinc nickelbecome contaminated with the anions of the nickel salts such as sulphateintroduced into the solution by means of replenishment and withcarbonate from solution contact with air. These anions contribute toburning of the deposit in the high current density areas reducing theoperable current density range, which can lead to the solutioneventually being unusable. This anion contamination is particularlydeleterious for plating solutions utilized for rack operation wheresolution turnover is minimal and the used current density range is wide.Current practice either involves replacement or dilution of the solutionto reduce contamination of these anions. For rack plating, precipitationof carbonate and sulfate by cooling a portion of the plating solution isusually insufficient to produce a wide enough operable current densityrange. Deposits of suitable appearance can be obtained by producingalloys containing greater than 15% nickel, but these are not desirablewith regard to corrosion performance.

It is a shortcoming of the prior art in alkaline zinc nickel platingthat certain components of the composition, particularly the oligomericor polymeric amine complexants used in many of the patents referencedabove, strongly adsorb on the cathode surface during the plating processand inhibit the effectiveness of the other additives, especially thepolyquaternary amine compounds described above.

It is accordingly, an object of the present invention to provide analkaline zinc nickel alloy electroplating bath in which electroplatedcoatings with even brightness, improved deposit distribution thickness,good resistance to burning, and high cathode efficiency may be obtainedin a wide range of current density even in the presence of pollutinganions such as carbonate and sulfate.

It is another object of the present invention to provide such anelectroplating bath which permits electroplating at a high currentdensity and at a shortened electroplating time.

Another object of the present invention is to provide an alkaline zincnickel alloy electroplating bath which may contain a wide range of zincconcentration levels for different plating operations.

It is also important, and an object of the present invention, that thezinc nickel plating bath be operable in manual, automatic rack andbarrel plating operations.

Other objects and advantages will be apparent from the followingdescriptions.

SUMMARY OF THE INVENTION

The present invention is thus concerned with electrodeposition on avariety of electrically conducting substrates in a medium which seeks toprovide improved cathode efficiency and/or improved brightness andleveling, and further to provide coatings that are resistant topost-plate “blistering”. Suitable substrates include iron andferrous-based substrates (including both iron alloys and steels),aluminum and its alloys, magnesium and its alloys, copper and itsalloys, nickel and its alloys, and zinc and its alloys. Aluminum and itsalloys and ferrous-based substrates are particularly preferredsubstrates, with steels being most preferred.

According to the present invention, there is provided an additive for analkaline zinc nickel alloy electroplating bath medium, the additivecomprising a urylene quarternary anmonium based polymer. It has beendiscovered that a zinc nickel alloy electroplating bath containing aneffective additive amount of a urylene quarternary ammonium basedpolymer accomplishes the objects of the present invention when used inconjunction with non-polymeric complexants. A polymer that is preferredby the present invention because of its effectiveness in enabling theplating bath to plate over a wide range of current densities is Urea,N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis[2-chloroethane]. Another polymer that is preferred is Urea,N,N′-bis[3-(dimethylamino)propyl]-, polymer with 1,4-dichlorobutane.Others include random copolymers comprising the reaction product of (i)one or more di-tertiary amines, including an amide or thioamidefunctional group and (ii) one or more second di-tertiary aminesincluding an unsaturated moiety with (iii) one or more first linkingagents capable of reacting with said amines (i) and (ii). Such usefulrandom co-polymers are disclosed in U.S. Pat. No. 7,109,375, theteaching of which are incorporated herein in their entirety. Themolecular weights of these urea based polymers must only be small enoughthat they are bath soluble. It is not believed that the functionality ofthe polymer is significantly affected by its molecular weight assumingthat the polymer itself is still sufficiently soluble. Generally, thepolymers useful in this invention include at least one urea basedpolymer of the form of either (a) Urea,N,N′-bis[3-at(dialkylamino)alkyl]-, polymer with 1,4 [2-haloaklane] or(b) Urea, N,N′-bis[3-(dialkylamino)alkyl], polymer with1,1′-oxybis[2-haloalkane], wherein for (a) or (b) the alkyl functionalgroups are selected from the group consisting of methyl, ethyl, proply,butyl, pentyl, and hexyl and the halogen functional group is selectedfrom the group consisting of chloro, bromo, fluoro, and iodo. Otheruseful polymers include the random co-polymers described above.

The non-polymeric complexants that are preferred by the presentinvention include trimethanolamine, triethanolamine, tripropanolamine,or N,N,N′,N′ tetrekis-hydroxyisopropylethylenediamine. It is alsopreferable that at least two of these complexants are concurrently usedin the bath.

The improved baths exhibit many advantages over the baths of the priorart, including even deposit appearance, effective plating at a highcurrent density, uniform plating thickness, and high cathode efficiency.It is particularly advantageous that the improvements of the presentinvention result in uniform plating thickness because it is a well knowndeficiency in the prior art that uniform plating thickness is difficultwhen the objects being plated comprise complex shapes with small ridgesand surface variations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The use of polycationic polymers in zinc plating solutions is well knownand has been utilized in zinc plating systems for many years. Thesepolymers are generally able to produce processes that yield metalplating that is resistant to burning and pitting and exhibit a highlyuniform metal distribution. Polycationic polymers are also used in thedeposition of zinc iron and zinc cobalt deposits where the complexantused to hold the iron or cobalt in solution is typically sodiumheptonate, sodium gluconate, or sodium tartarate. Examples of such bathsthat are able to plate both zinc and zinc alloys are disclosed in U.S.Pat. No. 4,983,263 to Yasuda et al, the content of which is hereinincorporated by reference. However, polycationic polymers have not beenthought to be effective in zinc nickel plating electrolytes. It isdesirable and widely sought throughout the plating industry to producedeposits of zinc nickel alloy containing 12% to 15% nickel. Theseprocesses generally suffer from several problems including non-optimalplating uniformity and low brightness and cathode efficiency.

It has been discovered that the combination of certain amino basedcomplexants and urea based polycationic polymers, rather than the usualoligomeric or polymeric amine complexants and epichlorohydrin basedpolycationic polymers, greatly improves the quality of zinc nickelelectroplated deposits. Surprisingly, it has been found that solutionsthat do not contain polymeric or oligomeric complexants, but whichutilize the complexants taught by the present invention, are responsiveto certain based polymers and result in a greatly improved zinc nickelplating process. Prior to the present invention, the polymeric oroligomeric complexants used in zinc processes interfered with thefunctioning of the polycationic polymers.

This improved process gives similar metal thickness distributioncharacteristics to zinc plating but which can contain the desirablefeatures of a zinc nickel alloy. A similar resistance to burning orpitting between the zinc and zinc nickel processes is also observed evenin the presence of interfering anions such as carbonate and sulfate. Thefinal result is that a zinc nickel process utilizing the additives ofthis invention can be operated to produce zinc nickel alloys containing12% to 15% nickel still retaining the good deposition characteristicsand extended operable current density range which was heretofore onlyachievable with a pure zinc plate.

Alkaline zinc electroplating baths, both containing cyanide ions andcyanide free baths, are well known in the art and have been commonlyused for years. The basic alkaline zinc electroplating bath contains azinc compound and an alkali hydroxide. Zinc can be introduced into theaqueous bath by any soluble zinc salt, but zinc oxide is the salt mostoften and most preferably used. The alkali hydroxide is generally eithersodium hydroxide or potassium hydroxide. At high pH ranges, it isgenerally thought that the zinc ions from the zinc salt are transformedinto a zincate ion, and thus zincate ions are generally present in aworking alkaline zinc plating bath. It will be appreciated that as usedherein, the term “zinc ion” includes zincate or other ionic speciescontaining zinc atoms useful in electroplating baths for electroplatingmetallic zinc and zinc alloys.

Zinc alloy electrolytic baths also contain salts of other metals, whichare generally nickel, cobalt, or iron. The present invention dealsspecifically and most preferably with zinc nickel alloy plating. Nickelis introduced into the zinc plating bath by means of any soluble nickelsalt. It is most preferable if this salt contains divalent nickel, andtherefore the most common and preferable nickel salts for use in thepresent invention are nickel (II) sulfate or nickel (II) acetate ornickel (II) carbonate.

The composition of the zinc nickel plating bath generally contains about5-25 g/L, but can contain up to 50 g/L or more, of zinc ions. Thiscontent is calculated on zinc ion concentration and would not beaffected by whatever corresponding anion (or cation) is used.Preferably, zinc is present in the solution at a concentration of about5-20 g/L. The alkaline hydroxide, preferably sodium or potassiumhydroxide, is generally present at a concentration of about 50 g/L to500 g/L or more, and is preferably about 70 to 100 g/L as sodiumhydroxide or 100 to 140 g/l as potassium hydroxide. Nickel is generallypresent in such baths from about 0.25-10 g/L, but is preferably in therange of 1-6 g/L.

Depending upon the purpose for which the electroplating is carried out,the zinc nickel bath can be used in widely different concentrationranges. For example, where increased throwing power is important, thedesirable zinc concentration is about 5 to 10 g/L, preferably 6 to 8 g/land about 70 to 140 g/l for the alkali hydroxide. When the currentefficiency and operability are important factors such as in barrelplating, the desired concentration of zinc is about 8 to 12 g/l and 80to 150 g/l alkali hydroxide.

In zinc nickel alloy baths it is important that the metal ions inappropriate amounts and in appropriate form be present in the bath. Onepreferred way is to use a chelating agent in the bath in an effectiveamount to maintain the metals, other than the soluble zinc, in the bathin solution, e.g., to dissolve the required amount of nickel and otheralloy ingredients in the bath. The chelating agent used herein shouldcomplex the nickel ions to an electrodepositable extent in a strongalkalinity of a pH of above 13 and thus permit their stable dissolution.It is an essential aspect of the present invention that appropriatecomplexants be used to effectively dissolve the nickel ions intosolution. By utilizing the preferred properties of the chelating agentstaught in this disclosure, unfavorable interaction between the chelatingagents and polycationic polymers can be avoided.

It has been found that the preferred chelating agents are selected fromthe group consisting of monoethanolamine, diethanolamine,trimethanolamine, triethanolamine, tripropanolamine, and N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine. However, it is believed thatthe functionality of the present invention can be achieved with anyamino alcohol or ethylenediamine based complexing agent provided that itis not polymeric. Additionally, it is most preferable to use acombination of triethanolamine and N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine as the nickel complexing agent.Typically, the chelating agent should generally only be present in theplating solution at a concentration high enough to ensure thedissolution of the nickel ions. Generally, levels of about 10-150 g/L ormore are employed and depend upon the concentration of nickel or otheralloying metal in a given bath.

The second essential aspect of the present invention is the use ofparticular polycationic polymers which aid in the plating process toproduce a better quality zinc nickel alloy plate. The incorporation ofthese materials gives the process a very high throwing power, whichresults in a uniform metal distribution, as well as aiding in producingplates that are resistant to burning and pitting. It has been found thatthe combination of polycationic based polymers with the above chelatingagents reduces an interfering effect at the surface of the platingallowing the polymers and other additives to adsorb onto the substratesurface and produce their favorable effect. The polymers that are ableto exhibit such a result are urylene quaternary ammonium based polymers,which include as polymers of the form Urea,N,N′-bis[3-(dialkylamino)alkyl]-, polymer with 1,4-[2-haloalkane] orUrea, N,N′-bis[3-(dialkylamino)alkyl]-, polymer with1,1′-oxybis[2-haloalkane] or Urea, N,N′-bis[3-(dimethylamino)propyyl)]-,polymer with 1,4-dichlorobutane. Other polymers useful in this inventioninclude random co-polymers comprising the reaction product of (i) one ormore di-tertiary amines, including an amide or thioamide functionalgroup and (ii) one or more second di-tertiary amines including anunsaturated moiety, with (iii) one or more first linking agents capableor reacting with said amines (i) and (ii). Such useful randomco-polymers are disclosed in U.S. Pat. No. 7,109,375, the teachings ofwhich are incorporated herein by reference in their entirety. A polymerthat is preferred by the present invention because of its effectivenessin enabling the plating bath to plate over a wide range of currentdensities is Urea, N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis[2-chloroethane]. Another polymer that is preferred is Urea,N,N′-bis[3-(dimethylamino)propyl]-, polymer with 1,4-dichlorobutane andothers such as Urea, N,N′-bis[3-(dimethylamino)propyl)]-, polymer with1,4-dichlorobutane andN′-[3-(dimethylamino)propyl]-N,N′-dimethyl-1,3-propanediamine,N-[2-hydroxy-3-(2-propenyloxy)propyl) derivatives. These polymers arepreferably incorporated into the bath by preparing a stock aqueousconcentrate made up at about 25-300 g/L, however this is optional and itis possible to directly add the polymer to the bath. In the operatingzinc nickel alloy plating bath, the urea based polymer is preferablypresent in an amount of up to about 20 g/L, more preferably 0.01 g/L to7 g/L, and most preferably at a concentration of about 0.1-2 g/L.

The zinc nickel alloy electroplating bath of the present invention canbe utilized to obtain uniform coatings over a wide range of currentdensities, which are additionally resistant to burning and pitting.These results are obtainable even if the concentrations of thecomponents change to a reasonable degree. It is the ability to effect auniformly thick coating of zinc-nickel alloy under different currentdensity that forms one of the primary advantage of the presentinvention.

In order to further illustrate the composition and process of thepresent invention, the following examples are provided. It will beunderstood that the examples are provided for illustrative purposes andare not intended to be limiting of the scope and the present inventionas herein described and is set forth in the claims.

EXAMPLE 1

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 90 g/L sodium hydroxide, 8 g/L zinc ions, 4 g/lnickel ions, 68 g/L triethanolamine, 30 g/L N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine, 12.5 g/l sodium silicate, and400 mg/L Urea, N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis[2-chloroethane]. At a temperature 30 C a bright steel Hullcell panel was plated for 20 minutes at 1 A in a Hull cell using anickel anode. The plated panel appearance was uniformly bright with novisible defects. The deposit thickness and nickel alloy content shown inTable 1 below was measured at current densities 4 A, 2 A, 0.5 A persquare decimeter across the plated panel using a Fischerscope X-raysystem XDL-B.

EXAMPLE 2

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 90 g/L sodium hydroxide, 8 g/L zinc ions, 4 g/lnickel ions, 68 g/L triethanolamine, 30 g/L N₃N,N′,N′tetrakis-hydroxyisopropylethylenediamine, 12.5 g/l sodium silicate, and100 mg/L Urea, N,N′-bis[3-(dimethylamino)propyl)]-, polymer with1,4-dichlorobutane andN′-[3-(dimethylamino)propyl]-N,N′-dimethyl-1,3-propanediamine,N-[2-hydroxy-3-(2-propenyloxy)propyl) derivatives. At a temperature 30 Ca bright steel Hull cell panel was plated for 30 minutes at 1 A in aHull cell using a nickel anode. The plated panel appearance wasuniformly bright with no visible defects. The deposit thickness andnickel alloy content shown in Table 1 below was measured at currentdensities 4 A, 2 A, 0.5 A per square decimeter across the plated panelusing a Fischerscope X-ray system XDL-B.

EXAMPLE 3

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 120 g/L potassium hydroxide, 8 g/L zinc ions, 4 g/lnickel ions, 68 g/L triethanolamine, 30 g/L N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine, 12.5 g/l sodium silicate, and100 mg/L Urea, N,N′-bis[3-(dimethylamino)propyl)]-, polymer with1,4-dichlorobutane andN′-[3-(dimethylamino)propyl]-N,N′-dimethyl-1,3-propanediamine,N-[2-hydroxy-3-(2-propenyloxy)propyl) derivatives. At a temperature 30 Ca bright steel Hull cell panel was plated for 30 minutes at 1 A in aHull cell using a nickel anode. The plated panel appearance wasuniformly bright with no visible defects. The deposit thickness andnickel alloy content shown in Table 1 below was measured at currentdensities 4 A, 2 A, 0.5 A per square decimeter across the plated panelusing a Fischerscope X-ray system XDL-B.

EXAMPLE 4

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 90 g/L sodium hydroxide, 12 g/L zinc ions, 4.5 g/lnickel ions, 60 g/L triethanolamine, 12.5 g/l sodium silicate, and 400mg/L Urea, N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis[2-chloroethane]. At a temperature 30 C a bright steel Hullcell panel was plated for 30 minutes at 1 A in a Hull cell using anickel anode. The plated panel appearance was uniformly bright with novisible defects. The deposit thickness and nickel alloy content shown inTable 1 below was measured at current densities 4 A, 2 A, 0.5 A persquare decimeter across the plated panel using a Fischerscope X-raysystem XDL-B.

COMPARATIVE EXAMPLE (EXAMPLE 5)

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 110 g/L sodium hydroxide, 8 g/L zinc ions, 700 mg/lnickel ions, 8 g/L tetraethylenepentamine, 2 g/l triethanolamine, 15 g/LN,N,N′,N′ tetrakis-hydroxyisopropylethylenediamine, 4 g/l sodiumsilicate and 50 mg/L N-benzyl nicotinamide. At a temperature 30 C abright steel Hull cell panel was plated for 20 minutes at 1 A in a Hullcell using a nickel anode. The plated panel appearance was uniformlybright from the low led to 4 asd and beyond 4 asd was dull showing acoarse grained deposit. The deposit thickness and nickel alloy contentshown in Table 1 below was measured at current densities 4 A, 2 A, 0.5 Aper square decimeter across the plated panel using a Fischerscope X-raysystem XDL-B.

COMPARATIVE EXAMPLE (EXAMPLE 6)

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 110 g/L sodium hydroxide, 8 g/L zinc ions, 700 mg/lnickel ions, 8 g/L tetraethylenepentamine, 2 g/l triethanolamine, 15 g/LN,N,N′,N′ tetrakis-hydroxyisopropylethylenediamine, 4 g/l sodiumsilicate, 400 mg/L Urea, N,N′-bis[3-(dimethylamino)propyl]-, polymerwith 1,1′-oxybis[2-chloroethane] and 50 mg/L N-benzyl nicotinamide. At atemperature 30 C a bright steel Hull cell panel was plated for 20minutes at 1 A in a Hull cell using a nickel anode. The plated panelappearance was uniformly bright with no visible defects. The depositthickness and nickel alloy content shown in Table 1 below was measuredat current densities 4 A, 2 A, 0.5 A per square decimeter across theplated panel using a Fischerscope X-ray system XDL-B.

COMPARATIVE EXAMPLE (EXAMPLE 7)

An aqueous electrolytic bath suitable for plating zinc nickel alloy wasprepared containing 90 g/L sodium hydroxide, 8 g/L zinc ions, 4 g/lnickel ions, 68 g/L triethanolamine, 30 g/L N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine and 12.5 g/l sodium silicate.At a temperature 30 C a bright steel Hull cell panel was plated for 20minutes at 1 A in a Hull cell using a nickel anode. The plated panelappearance showed three distinct bands. The first band from the HCDregion beyond 5 asd showed a coarse grained deposit, the second bandfrom 5 asd down to about 0.5 asd was semi bright to dull and the thirdband below 0.5 asd was bright. The deposit thickness and nickel alloycontent shown in Table 1 below was measured at current densities 4 A, 2A, 0.5 A per square decimeter across the plated panel using aFischerscope X-ray system XDL-B.

TABLE 1 Thickness (microns) and alloy % Ni A:C Example 4asd (A) 2asd (B)0.5asd (C) ratio 1 3.5 um/12.8% 2.5 um/12.6% 1.7 um/12.8% 2.06:1 2 4.2um/13.2% 3.0 um/12.1% 2.0 um/13.0% 2.10:1 3 5.3 um/13.4% 3.9 um/13.3%2.5 um/12.5% 2.12:1 4 6.0 um/12.9% 4.7 um/12.7% 2.9 um/12.2% 2.07:1 510.3 um/14.1%  6.5 um/13.2% 2.9 um/13.3% 3.55:1 6 8.9 um/15.2% 5.9um/13.6% 2.4 um/12.7% 3.71:1 7 11.0 um/14.5%  8.0 um/15.0% 3.5 um/14.4%3.14:1

It can be seen from these results that the novel process of the presentinvention, which is exhibited by examples 1-4, plates zinc nickel alloyswith a much improved deposit distribution compared to those baths thatdo not utilize the combination of a relevant urea based polymer incombination with a non-polymeric and non-oligomeric complexant, whichare exhibited by examples 5-7. Example 5 is a bath containing theoligomeric based amine complexant tetraethylenepentamine and Example 6is the same bath as Example 5 with a polycationic polymer.

While the invention has been described and illustrated herein byreferences to various specific materials, procedures, and examples, itis understood that the invention is not restricted to the particularmaterials, combinations of materials, and procedures selected for thatpurpose. Numerous variations of such details can be employed, as will beappreciated by those skilled in the art. It is therefore intended thatthe appended claims cover all such equivalent variations as fall withinthe true spirit and scope of the invention.

1. An alkaline aqueous electrolytic bath capable of electrodeposition ofa zinc-nickel alloy comprising: (i) 5-25 g/l zinc ions; (ii) 0.25-10 g/lnickel ions; (iii) 50-500 g/l of sodium or potassium hydroxide; (iv) atleast one non-polymeric complexing agent capable of complexing thenickel ions selected from the group consisting of monoethanolamine,diethanolamine, trimethanolamine, triethanolamine, tripropanolamine andN, N, N′, N′ tetrakishydroxyisopropylethylene diamine; and (v) at leastone urea based polymer selected from the group consisting of (a) urea,N,N′-bis[3-(dialkylamino)alkyl]-, polymer with 1,4-[2-haloalkane], (b)urea, N,N′-bis[3-(dialkylamino)alkyl]-, polymer with1,1′-oxybis[2-haloalkane], wherein for (a) or (b) the alkyl functionalgroups are selected from the group consisting of methyl, ethyl, propyl,butyl, pentyl, and hexyl and the halogen functional group is selectedfrom the group consisting of chloro, bromo, fluoro, and iodo, and (c)random co-polymers comprising the reaction product of (1) one or moredi-tertiary amines, including an amide or thioamide functional group,and (2) one or more second di-tertiary amines, including an unsaturatedmoiety, with (3) one or more first linking agents capable of reactionwith said amines (1) and (2); wherein the pH of the bath is above 13 andthe bath contains no polymeric complexants.
 2. The alkaline aqueouselectrolytic bath according to claim 1 wherein the non-polymericcomplexing agent is selected from the group consisting ofmonoethanolamine, triethanolamine, and N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine.
 3. The alkaline aqueouselectrolytic bath according to claim 1 further comprising more than onenon-polymeric complexing agent.
 4. The alkaline aqueous electrolyticbath according to claim 3 wherein the more than one non-polymericcomplexing agent comprises triethanolamine and N,N,N′,N′tetrekis-hydroxyisopropylethylenediamine.
 5. The alkaline aqueouselectrolytic bath according to claim 1 wherein the urea based polymercomprises urea N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis[2-chloroethane].
 6. The alkaline aqueous electrolytic bathaccording to claim 1 wherein the urea based polymer comprises is urea,N,N′-bis[3-(dimethylamino)propyl]-, polymer with 1,4-dichlorobutane. 7.The alkaline aqueous electrolytic bath according to claim 1 wherein thebath further comprises sodium hydroxide in an amount of about 50 g/L toabout 500 g/L.
 8. The alkaline aqueous electrolytic bath according toclaim 1 wherein the zinc ions are present in a concentration of about 2g/L to about 30 g/L.
 9. The alkaline aqueous electrolytic bath accordingto claim 1 wherein the nickel ions are present in a concentration ofabout 0.251 g/L to about 106 g/L.
 10. The alkaline aqueous electrolyticbath according to claim 1 wherein the at least one non-polymericcomplexing agent is present in a concentration of about 5 g/L to about150 g/L.
 11. The alkaline aqueous electrolytic bath according to claim 1wherein the urea based polymer is present in a concentration of about0.02 g/L to about 20 g/L.
 12. A method for electrodeposition of azinc-nickel alloy on a conductive substrate comprising the steps of: (a)contacting the conductive substrate with an alkaline aqueouselectrolytic bath comprising: (i) 5-25 g/l or zinc ions; (ii) 0.25-10g/l of nickel ions; (iii) 50-500 g/l of sodium or potassium hydroxide,(iv) at least one non-polymeric complexing agent capable of complexingthe nickel ions selected from the group consisting of monoethanolamine,diethanolamine, trimethanolamine, triethanolamine, tripropanolamine, andN, N, N′, N′ tetrakishydroxyisopropylethylene diamine; and (v) at leastone urea based polymer selected from the group consisting of (a) urea,N,N′-bis[3-(dialkylamino)alkyl]-, polymer with 1,4-[2-haloalkane] and(b) urea, N,N′-bis[3-(dialkylamino)alkyl]-, polymer with1,1′-oxybis[2-haloalkane], wherein for (a) or (b) the alkyl functionalgroups are selected from the group consisting of methyl, ethyl, propyl,butyl, pentyl, and hexyl and the halogen functional group is selectedfrom the group consisting of chloro, bromo, fluoro, and iodo, and (c)random co-polymers comprising the reaction product of (1) one or moredi-tertiary amines including an amide or thioamide functional group, and(2) one or more second di-tertiary amines, including an unsaturatedmoiety with (3) one or more first linking agents capable or reactingwith said amines (1) and (2); and (b) electrolytically depositingzinc-nickel alloy onto the surface of the conductive substrate; whereinthe pH of the bath is above 13 and wherein the deposited zinc-nickelalloy comprises 12-15 percent nickel and wherein the bath comprises nopolymeric complexants.
 13. The method according to claim 12 wherein thestep of electrolytcally depositing occurs with a cathode current densityin the range of about 0.1 ampere per square decimeter to about 25 ampereper square decimeter.
 14. The method according to claim 12 wherein thenon-polymeric complexing agent is selected from the group consisting ofmonoethanolamine, triethanolamine, and N,N,N′,N′tetrakis-hydroxyisopropylethylenediamine.
 15. The method according toclaim 12 wherein the at least one complexing agents comprisestriethanolamine and N,N,N′,N′ tetrekis-hydroxyisopropylethylenediamine.16. The method according to claim 12 wherein the urea based polymercomprises urea, N,N′-bis[3-(dimethylamino)propyl]-, polymer with1,1′-oxybis [2-chloroethane].
 17. The method according to claim 12wherein the urea based polymer comprises urea,N,N′-bis[3-(dimethylamino)propyl]-, polymer with 1,4-dichlorobutane. 18.The method according to claim 12 wherein the non-polymeric complexingagent is present in a concentration of about 5 g/L to about 150 g/L. 19.The method according to claim 12 wherein the urea based polymer ispresent in a concentration of about 0.02 g/L to about 20 g/L.